British Gas owner Centrica has extended two gas supply agreements, increasing the volume of gas it is buying from both Statoil and Gazprom.Centrica signed a 10-year agreement with Statoil in 2011 for the supply of 5bn cubic metres (bcm) of gas per annum to be delivered to the UK from October 2015.The extension of the deal now means that volumes will be increased to 7.3bcm per annum, equal to 73bcm over the agreement period.Meanwhile, Centrica has also raised the volumes agreed back in 2012 under a three-year deal with the UK division of Gazprom, Gazprom Marketing & Trading.It will now buy 4.16bcm per annum from GM&T over a total of six years, taking the total volume to 29.1bcm."Britain needs around 70bcm of natural gas each year to heat homes and businesses and to generate electricity, and the UK now needs to import more than half of this," Centrica said in a statement."The long-term supply agreements with Statoil and GM&T will meet the gas needs of 9m British homes every year and take the total amount that Centrica has committed in securing gas and electricity, through a range of suppliers, to over £50bn."Centrica was trading 0.9% lower at 275.74p by 15:10 on Wednesday.